Attack

This usually refers to the first stage of an envelope that occurs at the onset of a note, as it rises from 0 volts (silence when if controlling an amplifier module) to typically the value of maximum loudness. Percussive and plucked sounds have very fast attacks; slow, languid wind or string instrument phrases may have long attacks.

Trivia: A select few envelope generators allow an initial value other than zero; the attack phase of the envelope then proceeds from this initial value either to maximum or another specified value. This can be more realistic when imitating a sound such as a bowed string, as its volume rarely swells smoothly from absolute silence – there’s some minimum loudness caused by the initial contact of bow to string, and then it gets louder from there as the player digs in.